1. Field of Invention
This invention relates to multidose, medical injection syringes used for the vaccination and treatment of livestock diseases. More specifically, it relates to a process and a closed handling and delivery system for those injectable animal health products used in syringes and how the dosage level administered to the patient is controlled or metered.
2. Description of Prior Art
Generally speaking, in multidose, pistol grip livestock syringes, the precise metering of the dosage dispensed is accomplished by restricting the stroke of the plunger rod. Heretofore, the stroke of the plunger rod has been controlled by mechanical systems incorporated into the syringe body and trigger mechanisms. Original designs of pistol grip syringes commonly include ratchet and pawl mechanisms, wherein the trigger is squeezed and a pawl attached to the trigger engages a ratchet, formed on the plunger rod. The plunger rod is then advanced forward to dispense the medicament from the barrel of the syringe.
Metering is accomplished by an adjustable stop attached to either the trigger, as is demonstrated in U.S. Pat. No. 3,110,310 to Cislak (1963), or to the syringe body as is shown in U.S. Pat. 4,014,331 to Head (1977). The adjustable stop restricts the forward movement or stroke of the plunger rod, therefore metering the amount of medicament dispensed. Similar mechanisms for dosage metering are employed when pre-filled cartridges are used with pistol grip syringe bodies as is shown in U.S. Pat. No. 4,738,664 to Prindle (1988) and U.S. Pat. No. 3,517,668 to Brickson (1967).
Phillips et al. (1988), in U.S. controlled by a threaded adjustment on the anterior end of the syringe body. Other known cartridge type systems generally utilize a single dose system wherein one full squeeze of the trigger dispenses the entire contents of the cartridge as is shown in U.S. Pat. No. 4,576,591 to Kaye et al. (1986) and U.S. Pat. No. 4,968,303 to Clarke et al. (1990).
With those methods of dosage metering, the amount of medicament dispensed from a multi-dose cartridge is determined by a setting or an adjustment made to the syringe or applicator by the technician. Mechanical dosage settings are often bumped or may slip to the next setting so that many animals may be injected with the improper dosage before the mistake has been detected and the correction is made. It is also not uncommon for the technician to accidentally set the dosage adjustment to an improper setting. Most medicaments have a prescribed dosage level, which technically could eliminate the need for dosage adjustment by the technician.
There has not heretofore been provided a self-metering cartridge system or a system for automatically metering a predetermined dosage of a medicament from a cartridge.